How do you export a blender file as an .avi file in Blender 2.74?
In order to export your video edit to a new AVI file, you need to:


Set your Render Settings to a movie format that supports AVI
Click the Render Animation button.


As long as you have the Sequence checkbox selected in the Post Processing panel, it should render out your video edit to a new video file.

There are a number of Movie formats that also support the AVI encoding format.

They include:


AVI JPEG
AVI Raw
H.264 (with AVI format selected)
MPEG (with AVI format selected)
Xvid (with AVI format selected)